In general, a turbocharger used for supercharging of an internal combustion engine is provided with a waste gate valve at a turbine part which is configured so as to bypass a part of exhaust flow without passing through a turbine wheel, for supercharging pressure control. In a patent document 1, as a driving mechanism for the open/close driving of the waste gate valve, a so-called swing type mechanism is disclosed in which the linear motion of a rod of an electric actuator is converted to the rotational motion of a rotation shaft through a link and then a poppet type valve body which is supported on the distal end of an arm fixed to the rotation shaft oscillates.
In such the above waste gate valve, as described in the patent document 1, a small clearance exists between the distal end of the arm and the valve body which oscillate interlocking with the actuator, and it becomes a factor of the occurrence of abnormal sound. This abnormal sound can be suppressed by interposing a spring member, such as a conical washer, into the clearance. However, since the clearance has a function to bring the valve body into tight contact with a seat surface with a small degree of freedom to the posture of the valve body when the valve body is seated on the seat surface, by interposing the spring member, sealability at the time of full closing is reduced.